How Do I Get Rid of Thyronectria Cankers On My Honeylocust Trees?

There’s a threat creeping along the Front Range and preying on our Denver Honeylocust trees. Thyronectria cankers are more prevalent than ever and can stay under the radar long enough to do irreversible damage to trees and shrubs. Find out more about canker diseases and how to get rid of Thyronectria cankers on your trees.

What Are Thyronectria Cankers?

Cankers, in general, are a form of tree disease. A ‘canker’ is a visible injury on the outer part of the tree and is usually the result of an open wound that has become infected with fungi or bacteria. Thyronectria cankers are caused specifically by the fungus Thyronectria. 

All types of cankers are destructive and can spread easily, but different tree species are susceptible to different kinds of cankers. Thyronectria cankers present most often on honeylocust trees and are often confused with these common tree canker diseases:

  • Cytospora canker: found on spruce, pine, poplars, and willows.
  • Phomopsis canker: found on juniper, Russian olive, Douglas-fir, and arborvitae. 
  • Nectria canker: found on honey locust, oak, and maple.

You might be wondering, what exactly does a canker look like? You don’t need a microscope or binoculars to spot Thyronectria cankers. An injured area typically has a bumpy, cushion-like texture that is light yellow-brown or reddish-brown when fresh, but blackens with time.

Diseased spots are normally located in bark openings where raised areas of bark function as breathing pores. Patches of the tree trunk where the bark has thinned are also susceptible to cankers as well. 

Not feeling confident in your ability to diagnose your trees? No problem! Let our expert arborists take the guesswork out of it. They can spot Thyronectria cankers from a mile away!

What Kind of Damage Can Thyronectria Cankers Do To My Trees?

Canker diseases pose a serious threat to your trees and shrubs. When left unattended,  Thyronectria cankers can prove to be fatal. When a tree or shrub becomes infected, the cankers deal damage by cutting off the flow of essential nutrients to branches and strangling them. When girdled and deprived of necessary nutrients, individual branches begin to suffer from dieback. If cankers spread to the main trunk of the tree, it is likely that the entire tree will perish. 

That sounds like a lot of doom and gloom, but there are symptoms that should raise the alarm long before things ever get that serious! Cankers work slowly and steadily, taking months or even years to develop enough to girdle twigs and branches. To stop Thyronectria cankers in their tracks, keep a watchful eye out for these symptoms of the disease:

  • reduced foliage
  • yellowing and wilting of foliage
  • premature fall coloration
  • early leaf drop
  • yellow-brown or reddish-brown lesions
  • bark injuries that are oval and slightly sunken with callus ridges
  • bark splits between diseased and the healthy tissue, oozing sap or moisture
  • black inner bark that emits a foul odor

Once the Thyronectria canker disease has taken hold, spread throughout the wood, and infected even the base of the tree there’s nothing you can do to save it. If you even suspect that any of these symptoms are presenting in your trees and shrubs, call on our trained arborists to do a consultation ASAP!

When And How Do Thyronectria Cankers Spread?

There is a natural disease cycle that Thyronectria cankers follow. Understanding this cycle can help you both prevent and stop the spread of fungus amongst your trees and shrubs. 

Let’s take a look at the lifecycle of the Thyronectria fungi. The fungi responsible for the infection and disease overwinter, or stay alive in the cold months, on infected trees as vegetative material and fruiting (reproductive) structures. Thyronectria fungi can live in dead tree tissue, and as a result, they can produce spores on dead wood such as branch stubs, wound edges, or firewood. Come springtime, high humidity and wind-driven rain promote spore release, carrying the infectious pathogens to further the spread of the disease. 

All Canker-related diseases are most common on trees and shrubs under stress. Do trees get stressed? Sure they do! A distressed tree is any tree whose health and defenses are down. Consider the physical ramifications for your body when you are under a great deal of stress; your body is prone to catch a cold, develop a fever, and generally have a tough time fighting off infection. The same holds true for trees and shrubs.

What stresses a tree out? The Morton Arboretum cites a whole host of possibilities:

  • transplant shock
  • drought
  • winter injury
  • lack of nutrients from soil imbalance
  • overwatering
  • prolonged exposure to extremely high or low temperatures
  •  flooding
  • summer or winter sunscald
  •  hail
  • high winds
  • nutritional imbalances
  • soil compaction
  • mechanical injuries (lawnmower, vehicles)
  • animal damage
  • pruning wounds
  • root rot
  • insect borers

Injured and stressed trees are highly susceptible to Thyronectria canker disease because they tend to have open wounds which provide an entry site for opportunistic fungi and they don’t have the strength to fight it off.

Spread and infection peaks during wet and damp weather, particularly in fall and spring. The best way to prepare for the possible preying of fungi is to keep your trees at the top of their game, in full health. Strong, healthy trees have a high immune system and can ward off infection from Thyronectria fungi.

Ask us more about how to keep your trees in tip-top shape! We’d be happy to help with a free consultation.

Which Denver Trees Contract Thyronectria Cankers?

Some Denver trees are more susceptible to Thyronectria cankers than others. Newly planted or transplanted trees are always at high risk because they are still acclimating and are not yet fully established. The key Denver tree species to watch is the Honeylocust. Thyronectria cankers are notorious for destroying Honeylocusts in the Colorado front range area.

Do you have Honeylocusts on your property? Knowledge is the key to working on a successful preventative care plan. Check out these species details:

  • Honeylocust varieties can be thorny or thornless
  • This species is fast-growing and size at maturity varies widely, from 30′ – 70′ ft
  • The crown of the Honeylocust is open-spreading and filters light well
  • Honeylocusts can withstand a wide range of conditions including drought, high pH, and salt
  • This species is identifiable by its compound leaves with 8 to 14 leaflets 
  • Leaves are bright green in summer and clear yellow to yellow-green in the fall
  • In late spring and early summer fragrant, small flowers grow in clusters
  • Older Honeylocust trees have grayish-brown bark that is textured with long ridges and deep furrows

Because honeylocust trees are so susceptible to Thyronectria cankers, arbor experts highly recommend avoiding monogamous planting by using a diversity of trees. This is an important consideration for any Denver home or business owner planning major landscaping projects that involve new tree additions. 

Properly identifying the trees on your lot is no easy task. During a quick consultation on your property, our trained arborists can identify your tree species and inspect for any signs of Thyronectria cankers!

The Best Way To Treat Thyronectria Cankers

Research by the Colorado State University Extension admits that cankers are difficult to control, and ultimately the best way to treat them is with preventative control that keeps trees and shrubs healthy. Treatment programs instead should be customized, taking into consideration environmental factors like plant and soil conditions.

The CSU staff recommends the following tips and guidelines for preventing and treating cankers: 

  1. Prioritize preventing wounds and promoting tree vigor. Proper watering and fertilization routines in all seasons help boost tree health and strength. In addition, avoid stress caused by improper planting practices, drought, overwatering and insufficient area and oxygen for root growth.
  2. Injuries to the base of a honeylocust provide an entry point for fungi. Be careful when operating machineries like lawn mowers and weed trimmers, as they commonly cause basal injuries. Injuries to the stem and trunk, such as those caused by squirrel gnawing, pruning, and sunscald, can be minimized by removing loose bark and allowing the wound to air dry.
  3. Plant small trees such as 2 to 9 cm diameter trees (1 to 3 inches) will ensure successful establishment rather than planting large trees >10 cm (>4 inches). Water trees adequately with about 2.5 cm (1 inch) of water per week. Avoid over-watering trees since their roots need oxygen.
  4. Reduce the chance of other infections from Thyronectria cankers with prompt pruning of dead or infected branches and cutting out small cankers on main stems. Prune in cool, dry weather to minimize reinfection.
  5. If cankers are established, remove dead or dying bark and discolored wood ASAP. If the tree appears to be recovering, however, do not cut into healthy tissue. Wound dressings are not recommended. 
  6. To stop the spread of infection, disinfect all tools used to prune and cut. Dip in 70 percent rubbing alcohol or a 10 percent bleach solution and dry after each cut.
  7. Remove infected trees that are past the ability to treat, because canker fungi can grow on dead wood and produce spores that can infect nearby trees. Bury removed trees in a landfill or burn them within three weeks of cutting.

Properly diagnosing trees and shrubs for Thyronectria cankers can be very tricky. Let our experienced arbor experts help! We’ll determine the prognosis and create a treatment plan customized just for your needs to get your trees and plants back to good health.

Stop Thyronectria cankers in their tracks. Contact our expert arborists today for a free consultation!